1. Field of the Invention
The present general inventive concept relates to an inkjet printhead that ejects ink using a piezoelectric actuator, and a method of driving the piezoelectric actuator of the inkjet printhead.
2. Description of the Related Art
Generally, inkjet printheads are devices for printing an image on a printing medium by ejecting droplets of ink onto a desired region of the printing medium. Depending on an ink ejecting method, the inkjet printheads can be classified as a thermal inkjet printhead and a piezoelectric inkjet printhead. In the thermal inkjet printhead, ink is heated to form ink bubbles, and an expansive force of the bubbles causes ink droplets to be ejected. In the piezoelectric inkjet printhead, a piezoelectric crystal is deformed, and a pressure due to the deformation of the piezoelectric crystal causes ink droplets to be ejected.
FIG. 1 is a vertical section illustrating a conventional piezoelectric inkjet printhead. Referring to FIG. 1, the conventional piezoelectric inkjet printhead includes a flow channel substrate 10 and a nozzle substrate 20 to form a manifold 13, a plurality of restrictors 12, and a plurality of pressure chambers 11 as an ink flow channel. A plurality of nozzles 22 corresponding to the pressure chambers 11 is formed in the nozzle substrate 20. A piezoelectric actuator 40 is formed on the flow channel substrate 10. The manifold 13 is a passage allowing an inflow of ink from an ink reservoir (not shown) to the pressure chambers 11, and the restrictors 12 is a passage allowing and/or restricting the inflow of the ink from the manifold 13 to the pressure chambers 11. The pressure chambers 11 are arranged along one side or both sides of the manifold 13 to store ink to be ejected through the nozzles 22. A volume of the pressure chamber 11 varies according to an operation of the piezoelectric actuator 40. Thus, ink flows into or out of the pressure chamber 11 according to the pressure variation. A portion of the flow channel substrate 10, such as an upper wall thereof to define the press chamber 11 with the nozzle substrate 20, is used as a vibrating plate 14 to control the ink to flow in or out of the pressure chamber 11. The vibrating plate 14 is deformed by the operation of the piezoelectric actuator 40.
The piezoelectric actuator 40 includes a lower electrode 41, a piezoelectric layer 42, and an upper electrode 43 that are sequentially stacked on the flow channel substrate 10. A silicon oxide layer 31 is formed between the lower electrode 41 and the flow channel substrate 10 as an insulating layer. The lower electrode 41 is formed on the entire surface of the silicon oxide layer 31 as a common electrode. The piezoelectric layer 42 is formed on the lower electrode 41 above the pressure chamber 11. The upper electrode 43 is formed on the piezoelectric layer 42 as a driving electrode for applying a voltage to the piezoelectric layer 42. A flexible printed circuit (FPC) is connected to the upper electrode 43 for applying a voltage to the upper electrode 43.
When a driving pulse is applied to the upper electrode 43, the piezoelectric layer 42 is deformed, thereby bending the vibrating plate 14 and thus changing the volume of the pressure chamber 11. Ink contained in the pressure chamber 11 is ejected through the nozzle 22 according to the changed volume of the pressure chamber. The deformation of the vibrating plate 14 should be large enough to effectively eject ink having various viscosities. The deformation of the vibrating plate 14 depends on a deformation amount of the piezoelectric layer 42 in a transverse direction. The transverse deformation of the piezoelectric layer 42 depends on a transverse length of the piezoelectric layer 42 and a magnitude of the driving voltage applied to the piezoelectric layer 42. However, the transverse length of the piezoelectric layer 42 is restricted by a length of the pressure chamber 11 in a direction of the traverse direction. Therefore, in the piezoelectric actuator 40 shown in FIG. 1, the driving voltage to the piezoelectric layer 42 should be large enough to increase the deformation of the vibrating plate 14. Further, the transverse deformation of the piezoelectric layer 42 depends on a thickness uniformity of the piezoelectric layer 42. That is, if a thickness of the piezoelectric layer 42 is not uniform, the transverse deformation of the piezoelectric layer 42 is affected by a thickness variation thereof.